Bridging microstructure and crystallography with the micromechanics of cleavage fracture in a lamellar pearlitic steel

RK Barik and A Ghosh and MB Sk and S Biswal and A Dutta and D Chakrabarti, ACTA MATERIALIA, 214, 116988 (2021).

DOI: 10.1016/j.actamat.2021.116988

The present paper focuses on the microstructure-based cleavage crack propagation in a Charpy impact tested fully pearlitic steel by correlating microstructure and crystallography with the overall fracture behavior. The importance of pearlite lamellae orientation in providing preferred fracture paths is discussed, encompassing the mechanism of interface decohesion and stepwise crack propagation through a mathematical model simulation. While the 100 cleavage cracking is well familiar in pearlitic steels, crack propagation along the 110 crystallographic planes can also prevail in some pearlite colonies or nodules. This is related to suppressing the crack tip dislocation emissions due to restricted slip transferability across the lamellae interfaces. Besides, the strain incompatibility due to large elastic modulus or Schmid factor mismatch across the pearlite nodule boundaries is responsible for triggering internodular cracking in the steel. Connecting the framework of fracture mechanics with the experimental observations, the mechanisms pertaining to different types of tear ridges formed within a pearlite colony are proposed. This certainly illuminates the role of lamellae orientation in the process of crystal bending and shearing at the tear ridges formed within the colonies or at the twist nodule boundaries. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.